1. Field of the Invention
The present invention relates to a method of converting and displaying scan lines, including a reduction of pictures, for displaying interlace video signals for a television or the like represented by the NTSC standard on a non-interlace display apparatus such as a computer display and so on.
2. Description of the Related Art
For compressing a frequency band of television video signals of NTSC or the like, an interlace system is employed to divide one screen or one frame into two fields formed by even and odd scanning lines, respectively. On the other hand, display apparatuses for personal computers and so on employ in recent years a non-interlace system for preventing flickers on a picture. To display a picture for television on a display apparatus for personal computers or the like, therefore, an interlace video signal must be converted into a non-interlace signal and displayed after enlargement or reduction is performed if that required.
In this case, when the size of a picture is not changed, a non-interlace video signal is simply digitized into one frame, i.e., two fields of the picture, and once stored in a frame memory. The stored video signal is read out in synchronism with the frame period of a computer, converted into an analog video signal and displayed.
On the other hand, when the size of a picture is reduced for display, while this often achieved by simply thinning the scan lines to a half (one field), and further to a quarter (1/2 fields), the size reduction processing is performed by use of a frame memory for performing filtering processing between scan lines if a high image quality is required at an arbitrary reduction ratio.
In this way, conventionally, when display is performed at an arbitrary reduction ratio, one scan line for display is generated by converting a plurality of corresponding scan lines in an inputted video signal into a video signal of one scan line by the filtering processing. However, since an interlace video signal includes adjacent scan lines which exist in both the even field and the odd field, it need be processed in such a manner that a one-frame portion of the video signal is once stored in a frame memory, and scan line data is sequentially read out, filtered, and then written into a frame buffer for display, as described also in JP-A-64-591.